Missable: If you accidently delete any of the three codex's (Tanglegrove, Brinkreef or Rift) you can't get them back and you'll have to start a new game to create the Archvale Lexicon.To assemble the Archvale Lexicon you need to firstly collect all three codex's. These can be found in random surface chests in three different biomes. Ensure you search every square in each of following zones to find them:
1. The "Tanglegrove Codex" can be found in the
Jungle biome (Tanglegrove).
2. The "Brinkreef Codex" can be found in the
Underwater biome (Brinkreef).
3. The "Rift Codex" can be found in the
Lava/Volcanic biome (The Rift).
Once you've collected all three codex's, simply travel to any town that has a "Blacksmith Anvil" to craft the "Archvale Lexicon" and the achievement will pop.